This invention relates to optical waveguides and more particularly to a protective coating for such waveguides.
The increased burden on communication systems has fostered the development of high capacity systems using optical waveguides. These optical waveguides are constructed of a transparent dielectric material such as glass. They consist of a central core surrounded by a cladding having an index of refraction less than the index of refraction of the core. Light propagates along the waveguide. The theory of optical waveguides is contained in U.S. Pat. No. 3,157,726 Hicks et al and in a publication "Cylindrical Dielectric Waveguide Mode," by E. Snitzer, Journal of the Optical Society of America, vol. 51, No. 5, pp. 491-498, May 1961.
Recently, optical waveguides having very low attenuation per unit length have been developed. For example, the Maurer and Schultz, U.S. Pat. No. 3,659,915, "Glass Optical Waveguide," describes an optical waveguide comprising a cladding layer of pure fused silica or doped fused silica and a core formed of doped fused silica. The waveguides fabricated in accordance with Keck and Schultz, U.S. Pat. No. 3,711,262, are also suitable for use.
Optical waveguides require high strength for cabling processes and system installation. Waveguides often have surface flaws acquired through imperfections in the manufacturing process. Because almost all fractures start at these surface flaws, any process which improves the surface strength properties of the waveguide will also improve the overall strength. In addition, any process which prevents the introduction of surface flaws during abrasion will help preserve the strength. Fused glass waveguides fracture easily under tension because tension applied to the surface flaws causes very high stress concentration at their tips so that the intrinsic strength of the material is exceeded.
U.S. Pat. No. 3,962,515-- Dumbaugh, Jr. et al describes a strengthened optical waveguide.